The present invention relates to a piezoelectric/electrostrictive device. More particularly, the present invention relates to a piezoelectric/electrostrictive device which has, on a substrate made of a ceramic, at least one piezoelectric/electrostrictive layer made of a piezoelectric/electrostrictive ceramic composition containing, as a major component, a PbMg1/3Nb2/3O3—PbZrO3—PbTiO3 system composition and at least one pair of electrodes electrically connected to the piezoelectric/electrostrictive layer.
As a device capable of controlling a minute displacement in a submicron order, piezoelectric/electrostrictive devices have been known. In particular, a piezoelectric/electrostrictive device formed by laminating, on a substrate made of a ceramic, a piezoelectric/electrostrictive layer made of a piezoelectric/electrostrictive ceramic composition and an electrode layer to which a voltage is applied, is suitable for control of a minute displacement and moreover has superior properties such as high electromechanical transduction efficiency, high-speed response, high durability, low power consumption and the like. Therefore, the piezoelectric/electrostrictive device is in use in various applications such as piezoelectric pressure sensor, probe-transferring mechanism in scanning tunneling microscope, rectilinear guide mechanism in ultra-precision processing apparatus, servo valve for hydraulic system, head of VTR, picture device constituting flat panel type image display, head of ink jet printer, and the like.
Meanwhile, various investigations have been made on the piezoelectric/electrostrictive ceramic composition constituting the piezoelectric/electrostrictive layer of piezoelectric/electrostrictive device which is an important part of the device determining the properties of the device. In JP-B-44-17103 and JP-B-45-8145 are disclosed, for example, piezoelectric ceramic compositions wherein, in a Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 system composition (this composition may hereinafter be referred to as PMN-PZT system composition), part of Pb is substituted with Sr, La or the like.
Also in JP-B-42-23747 and JP-A-60-102779 are disclosed piezoelectric ceramic compositions wherein Ce is added to a PMN-PZT system composition in an amount of 0.1 to 7.0% by mass or 0.2 to 3.0% by mass.
These piezoelectric ceramic compositions were developed in order to achieve improvement in piezoelectricity, for example, improvement in mechanical quality factor or mechanical quality factor reduction in temperature dependent change of, etc. It was expected that a piezoelectric device of superior piezoelectricity could be provided by using such a composition.
In conventional piezoelectric/electrostrictive devices, various investigations were made on the properties of the piezoelectric/electrostrictive ceramic composition used therein. However, no investigation was made on a problem which a piezoelectric/electrostrictive material made of such a piezoelectric/electrostrictive ceramic composition, when laminated on a substrate, may give rise to interaction to the substrate, etc.
In fact, in a piezoelectric/electrostrictive device produced by laminating, on a substrate, a piezoelectric/electrostrictive material in which part of a PMN-PZT system composition is substituted with Sr, La or the like and then heat-treating the resulting laminate, the piezoelectric/electrostrictive layer has a low density owing to the restraint of the substrate, and there were problems in that the piezoelectric/electrostrictive layer gave a low flexural displacement, or, when a voltage was applied, the low-density portion of the layer gave rise to dielectric breakdown or short circuit.
Also in a piezoelectric/electrostrictive ceramic composition in which Ce is added to a PMN-PZT system composition, no investigation was made as to a problem arising interaction to a substrate, etc. Moreover, the composition per se had no sufficient piezoelectric/electrostrictive property. Particularly, it is the present state that the piezoelectric/electrostrictive property is low in the case that a piezoelectric/electrostrictive ceramic composition is a PMN-PZT system composition to which Ce is added in a relatively large amount.
In contrast, in JP-A-11-29357 is proposed a piezoelectric device produced by beforehand heat-treating a piezoelectric material composed mainly of a PMN-PZT system composition to produce a piezoelectric part and then adhering this piezoelectric part on a ceramic substrate to make dense the piezoelectric portion.
In this piezoelectric device, however, an inorganic or organic adhesive need be used in adhering the piezoelectric part on the ceramic substrate; therefore, there were problems that the adhesive impaired the transmission of oscillation between the substrate and the piezoelectric layer, or the properties of the piezoelectric layer and the substrate were deteriorated since adhesive components penetrated thereinto.